Britain may be basking in one of the hottest summers on record, but scientists now fear that the UK could face an abrupt switch to freezing winters and Icelandic summers.

Leading global warming experts suspect that climate change, instead of being a gradual and largely predictable process, could mean that Europe's weather patterns will worsen severely with very little warning.

At any time after 2010, their research suggests, Britain's average temperature could drop by up to 5C within as little as three or four years - with catastrophic results for farming, transport, northern towns and tourism.

That would leave Britain with the same average temperatures as Iceland, said Professor Jochem Marotze, one of Europe's leading oceanographers. "It would wreck agriculture the way we know it now," he said.

When southern Britain was sweltering with a record 38.1C (100.6F) last Sunday, residents of Iceland's capital, Reykjavik, endured rain and a much cooler 13C (55F).

Many scientists now believe that rapidly increasing CO2 emissions will exacerbate the natural cycle of hot and cold weather that led to the mini Ice Age of the 17th century by severely affecting natural ocean currents.

The natural cycle of hot and cold periods is chiefly responsible for this summer's heatwave, say climatologists. However, global-warming gases are very likely to have intensified its effects.